This invention relates to a method of grinding a workpiece into a cylindrical shape while taking advantage of electrolytic action.
In a conventional method of grinding a workpiece into a cylindrical shape, utilizing electrolytic action, or a so-called electrolytic grinding method, as shown in FIG. 1, it has been customary to grind the surface layer of a workpiece 2 to a predetermined depth of t by feeding the non-rotating workpiece toward the center of rotation of a grinding wheel 1 rotating at a high speed to the depth t, and then rotate the workpiece 2 one revolution at a low speed, so as to grind the surface layer of the workpiece to the predetermined depth t, whereby said workpiece 2 is ground into a desired cylindrical shape. In FIG. 1, reference numeral 5 designates an electrolyte supply nozzle and 6 designates a power source for the electrolysis.
However, the conventional method described above has had the disadvantage that, since the electrolytic grinding is terminated, with the center of the workpiece 2 in the position of its stroke closest to the center of rotation of the grinding wheel 2 and with said workpiece in contact with said grinding wheel, a land is formed by re-electrolysis at the portion of the workpiece where the electrolytic grinding was terminated or started, which degrades remarkably the circularity of the finished workpiece.
This disadvantage in the above described electrolytic grinding method occurs since the described workpiece 2 is fed toward the center of rotation of the grinding wheel 1 without rotation of the workpiece, and thereafter when the depth of cut becomes t, the ground depth of the workpiece at an initial grinding portion thereof is larger than that of the peripheral surface of the workpiece 2 in the electrolytic grinding thereof during one rotation of the workpiece. Thus, a concaved surface portion is formed at the peripheral surface of the workpiece where the grinding was started. Also, when the workpiece 2 is rotated one revolution and electric current is stopped, the portion at which rotation of the workpiece 2 is terminated corresponds to the starting portion of rotation, and the concaved surface portion of the workpiece is enlarged by re-electrolysis at this portion of the workpiece, which further degrades the circularity of the finished workpiece, thus, conventionally, this concaved surface portion of the workpiece 2 must be removed by mechanically regrinding the same, after the electrolytic grinding is terminated. However, as apparent from the Table described below, a comparison of the above described conventional process with the process of the invention shows that the working performance is low in the conventional process and the circularity is only of 0.026 mm at the utmost in the conventional process, as compared to a circularity of 0.0026 mm in the workpiece ground according to the present invention.